Recently, there is extensively used an endoscope whereby an elongated insertable part can be inserted into a body cavity to observe organs within the body cavity or various therapeutic treatments can be made, as required, by using a treating tool inserted through a treating tool channel.
Generally, there are provided sucking tube lines for sucking and removing a mucus, dirt and blood within a body cavity. Such sucking tube lines are divided into a first tube on the upper stream side from the operating part to the insertable part tip part of an ordinary endoscope and a second tube on the lower stream side from the operating part to the connector connected to the universal cord at the end. These tubes are connected at the respective ends positioned within the operating part to a suction switching part provided in the operating part and the second tube is connected at the other end to a suction pump so that a suction may be made by operating the suction switching part.
Conventionally, as disclosed, for example, in a U.S. Pat. No. 4,562,830, in such sucking tube lines, the inside diameter of the first tube and the inside diameter of the second tube have been equal to each other.
Now, the dirt and mucus must be sucked so quickly as to reduce the inspecting time to make the pain of the patient as small as possible. As a quickly sucking means, it is considered to increase the sucking capacity of the suction pump and further to enlarge the inside diameter of the sucking tube to make the resistance of the tube as small as possible. However, there are problems that, in case the sucking capacity of the suction pump is increased, the size of the pump will become large and the power consumption of the pump will increase. Also, in case the inside diameter of the sucking tube is made large, the outside diameter of the endoscope insertable part provided with this sucking tube will become large and a great pain will be given to the patient when the insertable part is inserted into the body cavity. Further, in case the inside diameter of the tube on the upper stream side is large, the sucked solid will clog the lower stream tube and no subsequent suction will be made.